Meanwhile opponents of unilateral USA action called an emergency closed-door meeting of the UN Security Council for Thursday.

The World Health Organization said on Wednesday that 43 people had died in Saturday's attack on Douma from "symptoms consistent with exposure to highly toxic chemicals", and more than 500 in all had been treated. "Get ready Russian Federation, because they will be coming, nice and new and 'smart!' You shouldn't be partners with a Gas Killing Animal who kills his people and enjoys it!"

But Mattis, at a congressional hearing on the Pentagon's 2019 budget request, declined to discuss military plans, saying just that legislative leaders would be notified before any attack was undertaken.

"Russia vows to shoot down any and all missiles fired at Syria", Trump wrote on Twitter.

"If they are serious in fighting terrorists, we're going to be partners, and I said not only the United States".

"Due to the recent security situation between USA and Syria, and as a precautionary measure", the airline said, "Middle East Airlines will be modifying the routing of some of its flights, which will affect their departure times".

He did not say whether France is planning military action against Assad's government.

The Jaish al-Islam group in Douma agreed on Sunday to withdraw, hours after a suspected chemical weapons attack on the town that has raised the prospect of U.S. strikes.

"Never said when an attack on Syria would take place".

The attack took place in eastern Ghouta, one of the last remaining strongholds of anti-government rebels in the country.

It has been observed in subsequent military deployments in Libya and Iraq and many British lawmakers and voters are deeply sceptical of deepening involvement in the Syrian civil war.

United Nations Secretary General Antonio Guterres on Wednesday said he had met with ambassadors from the five permanent members including Russian Federation and the United States, and "stressed the need to avoid the situation spiralling out of control".

"But we support everything that is being done to show that the use of chemical weapons is not acceptable", she added.

Macron has insisted he does "not want an escalation" and that any response would focus on Syria's chemical capabilities, not on allies of the regime.

The Foreign Ministry in Damascus denounced President Donald Trump's threat to attack the country as "reckless" and a danger to global peace and security.

Erdogan said Thursday Turkey was anxious by the "arm wrestling" of world powers over Syria.

"In response to media queries, the Spokesperson for the Organisation for the Prohibition of Chemical Weapons (OPCW) confirms that the OPCW Fact-Finding Mission (FFM) team is on its way to Syria and will start its work as of Saturday 14 April 2018", the organisation's statement reads.

The Syrian government and Russian Federation say the reports of a poison gas assault on the Syrian town of Douma are bogus.

She said the Syrian army's victory in Eastern Ghouta constituted a turning point in the course of the Syrian war.